In general, a seat provided rotatably relative to a vehicle body has its leg or the like provided with a latch device; this latch device is engaged with a rod-shaped portion of a striker fixed to the vehicle body, and the seat is thereby locked to the vehicle body. Such a latch device is configured, for example as disclosed in Patent Literature 1, such that a latch, a ratchet or any other rotatable part is supported by a base plate. The latch has a slot formed therein, and the slot is configured to receive the striker so that the latch is engaged with the striker.